Method for opening rigid fibers

ABSTRACT

A method of opening a tow of staple fibers wherein the fibers are first cut to a length of less than 254 mm. and which are then introduced into a gas stream emanating from a nozzle located in a tubular member having a fiber opening section. The gas stream having a velocity at the nozzle greater than 30 meters per second.

0 United States Patent 1151 3,694,862

Okuda et al. 1 1 Oct. 3, 1972 541 METHOD FOR OPENING RIGID [56] References c1161 FIBERS k ok as T k T daak. UNITEDSTATES PATENTS 0 0; B [72] Invent $3 K xatsi'lyuki Suga: 2,079,094 5/1937 Wh1tehead etal ..l9l.56 Wm Tgkyo anof Japan 2,402,203 6/1946 Pharo ..19/205 x 2,733,122 1/1956' Hereleetal. ..2s/72.14x 3,111,719 11/1963 Novotny ..19/200 [731 Ass1gnee- 3,432,892 3/1969 Case ..19/200 x 9 9 1 FOREIGN PATENTS OR APPLICATIONS 22 Filed: Jan. 16, 1970 1,127,176 9/1968 Great Britain ..19/200 [21] Appl- N0-: 13 Primary Examiner-Dorsey Newton Attorney-Sughrue, Rothwell, Mion, Zinn and Macpeak 30 Fore A lication Priority Data 1 pp 57 ABSTRACT Jan. 17,1969 Japan ..44/2933 V v r A method of openmg a tow of staple fibers wherein the fibers are first cut to a length of less than 254 mm. 521 US. Cl. ..19/.ss, 19/65 R and which are then introduced vinto a g stream 51 1m. 01. ..D0lg 1/04 emanating from a nozzle located in a tubular member 58 Field 61 Search ..19/.3-.6, 6s, 65 A, having a fiber P swim- The gas stream having a velocity at the nozzle greater than 30 meters per second.

2 Claims, 2 Drawing figures METHOD FOR OPENING RIGID FIBERS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of opening rigid fibers and more particularly to a method of opening a tow of rigid staple fibers by a high speed gas stream.

2. Description of the Prior Art Inorganic fibers such as glass fibers, asbestos, rock wools, ceramic fibers, metallic fibers, and carboceous fibers such as carbonized polyacrylonitrile fibers prepared by baking polyacrylonitrile fibers at about 300 C. have a large modulus but low ductility. Therefore, such fibers have a very high rigidity as well as being very brittle to bending.

Accordingly, a method which can be used for opening ordinary organic fibers is not applicable for opening a tow or staple of rigid fibers. For example, when the aforesaid inorganic fibers or carbonaceous fibers are opened by means of a garnett machine or roller guard machine, which is usually employed for opening organic fibers, the fibers are easily cut to thereby shorten the length of the fibers and because the fibers have a high resistance to bending and have a self-lubricating property, it is difficult to form a web of the fibers by intertwining the fibers with each other. This becomes an important problem in producing felts or non-woven cloths.

Also, recently in order to use fibers as fillers for metals or synthetic resins, it has frequently been required to open fibers shorter than 10 mm., however, the aforesaid difficulties have not yet been overcome.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method of opening fibers which uses a high speed turbulent flow of gas. The method of the present invention can be applied to any kind of fibers but in particular, it can be more effectively applied to fibers having a high rigidity but low ductility and which are brittle to bending and have weak strength at the nodes. Such fibers are inorganic fibers such as those of glass, asbestos, rock wool, slag wool, ceramic and carbonaceous fibers such as carbonized fibers. Also, the method of the present invention can be effectively used for opening lubricous fibers such as polytetrabluoroethylene. In addition, the fibers treated mainly by the method of this invention are tow or staple fibers cut into lengths shorter than 254 mm.

The method of the present invention will then be explained in detail by referring to the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view showing an embodiment of the present invention including one type of cutting device for cutting a length of staple fibers, and

FIG. 2 is a schematic view showing a fiber opening tube used in the method of the present invention.

DETAILED DESCRIPTION OF THE INVENTION In FIG. 1, raw material as previously mentioned is supplied through a feeder 1 from a cutting mechanism 5, by any suitable manner. The cutting mechanism 5 cuts the staple fibers into the desired lengths less than 254 mm. It is desirable to supply the fibers at as constant a speed as possible, that is, at a constant weight per unit time.

The fibers thus supplied are blown up through a fiber opening tube 2 by a high speed gas stream jet through a nozzle 3 disposed at the lower portion of the tube. The velocity of the stream is from between 30 m./sec. to the velocity of sound, whereby the tow of staple fibers are astonishingly opened into individual single fibers by the extremely turbulent flow of gas in the fiber opening tube without the use of any mechanical fiber opening means. In addition, the fibers thus opened are directed at random into a cyclone separator of a condensor. In

this case, the effect of fiber opening depends largely upon the structure of the fiber opening tube and the velocity of the flow of gas or air. It is necessary to utilize a turbulent flow and as the result of detailed investigations, the inventors have found that by varying the dimensions of the nozzle, the shape of the nozzle, and the velocity of gas flow at the nozzle, sufficient turbulent flow can be formed for opening the fibers.

Furthermore, by providing suitable buffer plates or gas turbulent plates 4 in the fiber opening tube as shown in FIG. 2 of the accompanying drawing, a turbulent fiow of gas can be obtained by the complicated passageway presented. The critical Reynolds number is varied according to each individual case and in any case it is desirable that the Reynolds number be sufficiently larger than the critical Reynolds number.

It is possible that the fibers passed through the fiber opening tube can be formed into a web of a desired thickness by means of a cyclone separator and a conveyor. Also, it is possible to form a web directly by connecting the fiber opening tube to a condenser cylinder type web forming means.

The invention will now be explained by the following examples.

EXAMPLE 1 A bundle of about 3,000 carbonaceous single fibers each having a diameter of 13 microns was cut into a length of 76 mm., supplied to the fiber opening machine having the fiber opening tube as shown in FIG. 1, and was opened by the using an air stream having a velocity at the nozzle of about 200 m./sec. The fibers thus opened were formed into a web having a surface density of 200 g./sq.m. by means of a cyclone system. The fiber opening rate was excellent and the fibers could be formed into an excellent felt by means of an ordinary needle punch machine. Moreover, in the method shown above, there was no loss of fibers observed such as the encountered when opening was performed by the ordinary mechanical manner.

EXAMPLE 2 A cylindrical member having a diameter the same as the inside diameter of the fiber opening tube and a height almost the same as the length of the diameter was cut into two portions along the height-wise direction to form semi-tubular turbulent members. The eight turbulent members were prepared and mounted in the fiber opening tube 2 so that the cut faces of the adjacent members 4 were at an angle of degrees to each other as shown in FIG. 2. A bundle of carbonaceous fibers having a larger rigidity than that of the fibers used in Example 1 and each having a diameter of 8 microns was supplied into the fiber opening machine set forth above. The bundle had been cut to a length of 50 mm. The opening of the fiber bundle was accomplished by using a gas stream having a velocity at the nozzle of about 20 m./sec., 30 m./sec., 80 m./sec., 160 m.lsec., or 340 m./sec. The opened fibers were withdrawn by means of a cyclone system and then formed into a web having a surface density of 30 g./sq. m. by a condensor system. The results showed that the fibers were sufficiently opened when the velocity of the gas was higher than 30 mJsec. Also, a thin web having a high uniformity was prepared from the fibers thus opened.

EXAMPLE 3 The fibers as in Example 2 were cut to a length of about 0.8 mm. and the mass of these short cut fibers was opened under the same conditions as set forth in Example 1. Powdered short fibers were obtained which had been sufficiently opened. The powdered short fibers could readily be dispersed uniformly in an emulsion of polytetrafluoroethylene from which an excellent composite article could be prepared.

What is claimed is:

l. A method of opening staple fibers comprising the steps of:

a. cutting a tow into staple fibers to a length of less than 254 mm.,

b. introducing said staple fibers into a moving gas stream, and

c. increasing the turbulence of said gas stream at a plurality of longitudinally spaced positions along the gas stream flow path downstream from the point of introduction of the cut fibers into said gas stream, wherein each increase at the localized areas of increased gas stream turbulence acts to assist in the opening of the cut fibers.

2. The method of opening a tow or staple fibers as set forth in claim 1 wherein said gas stream has a velocity, upstream of the point of introduction of the cut fibers, greater than 30 meters per second. 

1. A method of opening staple fibers comprising the steps of: a. cutting a tow into staple fibers to a length of less than 254 mm., b. introducing said staple fibers into a moving gas stream, and c. increasing the turbulence of said gas stream at a plurality of longitudinally spaced positions along the gas stream flow path downstream from the point of introduction of the cut fibers into said gas stream, wherein each increase at the localized areas of increased gas stream turbulence acts to assist in the opening of the cut fibers.
 2. The method of opening a tow or staple fibers as set forth in claim 1 wherein said gas stream has a velocity, upstream of the point of introduction of the cut fibers, greater than 30 meters per second. 